Copper corrosion inhibitor



Patented Feb. 16, 1943 refrigerator and turbine systems.

UNITED STATES PATENT UUKUI Ul l OFFICE 2,31 1,505 COPPER CORROSION INHIBITOR Francis M. Archibald, Elizabeth, N. .l., and Carl A. Harris, New York, N. Y.,-assignors to Standard Oil Development Company, a corporation of Delaware 2 Claims. ('01. 252-47) This invention relates to stabilized highly refined hydrocarbon oils of light lubricating oil consistency, commonly termed white oils, particular grades of which are employed as medicinal oils, textile oils and for uses in transformer,

The hydrocarbon base oils of the compositions prepared according to the invention are obtained by highly refining petroleum distillates of light lubricating oil consistency by means of treatment with successive volumes of fuming sulfuric acid followed by neutralization, washing and generally clay percolation or contacting. The oils refined in this manner largely consist of paraffin and naphthene hydrocarbons and range in color from about 16 to Saybolt and have a viscosity of above about 32 Saybolt-Universal seconds at 100 F. and preferably between about 55 and 350 seconds Saybolt Universal at 100 F. The highest grades of the oils so prepared are suitable as medicinal oils and are refined so as to. pass the specifications for petrola-tum liquidum U. S. P.

The extensive treatment of these oils imparts to them an objectionable characteristic in that upon exposure to metals such as copper at elevated temperatures staining of the metal occurs. This is a disadvantage in the case of oils, such as transformer and refrigerator oils, which in service come into contact with copper and similar metals. It has also been found that medicinal oils imparting a staining effect upon copper develop bad odors upon exposure to' sunlight. It has been proposed to repurify the oils as a means of combating this deterioration. Repurification, however, is generally considered not advantageous because such processing is expensive and somewhat uncertain as to its efficiency.

It has'now been found that certain agents may be added to these highly refined oils to. combat this development of corrosive properties at elevated temperatures of the various types of white oil products, especially with regard to copper. These compounds are also satisfactory addition agents to White oils in that they have suitable oil solubility, and they do not impart a detectable taste to the composites in the consentrations in which they are used. Also the compounds employed are relatively inexpensive and are added to the oils in very low concentration.

The amount of the compounds employed varies with the particular activity of the individual compound. The amounts are usually adjusted to lower the pH of the oil by 0.5 to 1.5 when a sample of the composite is agitated with an ejual volume of distilled water of pH about 5.5; it

appears as a consequence of this treatment that ionization occurs and that some hydrogen ions are transferred from the oil to the water, the latter which when tested gives a pH value of about 4.5. In no case are the compounds employed in a concentration greater than 0.05% but are usually employed in the lower amounts of the range from 0.01% to 0.0001%.

The compounds which have been found to be active as corrosion inhibiting agents in white oil compositions are the non-volatile, oil-soluble, relatively water-insoluble, organic compounds of acidic characteristic and of molecular weight above about 120. Of this class the acids and the corresponding amides are especially worthy of mention. The aliphatic compounds employed are relatively non-volatile at ordinary temperatures and preferably have a molecular weight above about 180. The suitable aromatic acid compounds are those having a molecular weight above about 120 and of these the monohydroxy acids are preferable. Acid compounds of very high molecular weight above about 300 are not employed because of their tendency to break down under service conditions of the white oil compositions. Compounds which have been found very satisfactory are stearic acid, maleic anhydride, salicyclic acid, anthranilic acid, tertiary amyl salicyclic acid, thymotic acid, dimethylglyoxime, stearamide, and saccharine. Of these compounds, stearic acid, salicyclic acid and their derivatives have been found to be especially advantageous. These compounds may be added directly to the oil or dissolved in a small amount of oil to make concentrate which is employed for blending into the oil.

The test usually employed to detect corrosion in white mineral oil products is to maintain the oil at 210 F. for about two hours in the presence of a highly polished copper strip. Any tarnishing or discoloration of the copper strip is considered as evidence of corrosive properties of the oil. Another test to which the finished oils are subjected is the hot acid test described in the U. S. Pharmacopoeia (9th edition, page 315). The material added must not be seriously affected in this test.

In order to illustrate the invention, the following examples are provided. The invention is not limited to these examples.

Example I A white mineral oil of viscosity -Saybolt Universal Seconds at F. was heated with a highly polished copper strip at 210 F. for two hours. The copper strip showed a dark red stain. The same oil to which had been added 0.01% stearic acid, when heated with a copper strip under the same conditions, showed no discoloration or tarnishing.

Example 11 A white mineral oil of viscosity 85Saybolt Universal seconds at 100 F., when heated with a highly polished copper strip at 210 F., for two hours, showed a dark blue peacock stain. A sample of the same oil to which had been added 0.001% of salicyclic acid, when heated with a copper strip under the same conditions, did not tarnish or cause any discoloration of the copper strip.

Example III A white mineral oil of viscosity 85-Saybolt Universal seconds at 100 F. giving a red peacock stain on polished copper heated to 210 F. when blended with 0.001% dimethyl glyoxime gave no staining efiect on polished copper over a 2 hour test at 210 F.

Example IV and imparted no taste to the blended oils.

While specific compounds have been mentioned as inhibitors towards the development in white oil products of corrosiv properties, it is not to be inferred that only the compounds mentioned are efiective for purposes of combating the corrosion. The corrosion of white mineral oils can also be prevented by mildly oxidizing a portion of the material so as to produce a small concentration of free acidity. Thus, by the addition of a small amount of an oxidized white oil material to a considerably larger volume of untreated white oil, it has been found that a product stable against the formation of products corrosive to copper at 210 F. is obtained. In this manner a composition is obtained which is satisfactory according toall the standard tests by which white oils are graded for the various uses to which they are particularly adapted.

Our invention is not limited to the use of the particular compositions shown, nor to any theory with regard to the activity of the ingredients, but only to the following claims in which it is desired to claim all the novelty inherent in the invention.

- We claim:

1. The method of decreasing the corrosive actionof mineral white oil compositions on copper which comprises incorporating saccharine in an amount between 0.5% and 0.0001% in a highly refined mineral white oil distillate, which is corrosive to copper, has a viscosity above about 32 Saybolt-Universa-l seconds at F. and has a color betweenabout 16 and 30 Saybolt.

2. The method of decreasing the corrosive action of mineral white oil compositions on copper according to claim 1 in which the saccharine is present in an amount from 0.01% to 0.0001%.

FRANCIS M. ARCHIBALD. CARL A. HARRIS. 

